The present invention relates to calorimeters for measuring the color content of light and has a response mimicking the response to color of the human eye, as may be represented by the CIE color matching functions. The invention is especially suitable for calibrating color monitors and color video displays, whether of the cathode ray tube or LCD type. The invention is also applicable generally for measuring the color characteristics of other sources (emissive or reflective) of illumination, such as the color temperature thereof.
It has been discovered in accordance with the invention that a colormetric response which accurately mimics the response to color of the human eye can be modeled with edge filters which pass the upper end of the visible spectrum and which are in overlapping relationship, when such filters are paired with photodetectors. The response can be digitally synthesized from the output of the photodetectors, The measurements made with the colorimeter may be used to calibrate a color monitor or display, utilizing techniques known in the art. The mechanical and electrical design makes the inventive colorimeter readily manufacturable at cost competitive with contemporary colorimeters, and also usable in a way compatible with the use of such contemporary colorimeters.
Accurate colorimetry has not been provided by contemporary calorimeters suitable for use by non-technical users and outside of a laboratory environment. As discussed in the text Measuring Colour, Second Edition by R. W. G. Hunt (published by Ellis Horwood Limited, 1991), contemporary colorimeters using filtered photo cells have not provided accurate colorimetry in that xe2x80x9c. . . it is usually impossible to find filters that, when combined with the spectral sensitivity of the unfiltered photo cell, result in a perfect match to the {overscore (x)}(xcex), {overscore (y)}(xcex), and {overscore (z)}(xcex) functions.xe2x80x9d Also as discussed in the Hunt text, even with narrow intervals over the visible spectrum and even with the use of optimized weights to minimize errors, accurate colorimetry 30 has not been achieved. (See, pages 178-181 of the Hunt text). Such calorimeters as discussed by Hunt are represented by Vincent, U.S. Pat. No. 5,272,518, issued Dec. 21, 1993, Suga, U.S. Pat. No. 4,150,898, issued Apr. 24, 1979, and Lutz, et al., U.S. Pat. No. 5,168,320, issued Dec. 1, 1992.
The present invention provides an improved filter colorimeter which utilizes edge filter as well as digital processing and enhancement to provide a response which mimics the human eye response so as to obtain accurate colorimetry.
The colorimeter provided by the invention also improves accuracy of colorimetry through the use of apertures which baffle the light being measured and limit off color, high angle emissions, which are common from LCD displays.
The mechanical and electro-optical structure of the calorimeter provided by the invention enables it to be used in a manner compatible with contemporary colorimeters, as well as to be manufacturable at a sufficiently low cost to be priced competitively with such colorimeters.
In accordance with the present invention, a color measuring device is provided The device includes a plurality of photodetectors for measuring light signals. A field programmable gate array coupled to the photodetectors reads data from the photodetectors in parallel.
In accordance the a more limited aspect of the present invention, the color measuring device includes a plurality of optical filter/photodetector pairs, preferably in an array in which each pair receives light over a field of view which is limited. Generally, the field of view is angularly constrained so as to prevent color-distorted, higher angle rays or emissions from the emissive surface from reaching the photodetectors. The pairs have a responsivity which extends over a different overlapping wavelength region at long wavelength ends of the visible spectrum. Edge filters may be used together with photodetectors, preferably providing digital outputs to obtain this responsivity. A translator which digitally processes the photodetector outputs converts the responsivity of the pairs into a responsivity mimicking the color matching functions representing the responsivity of the human eye. These may be the CIE Commission Internationale de l""Eclairage {overscore (x)}, {overscore (y)}, and {overscore (z)}functions from which the CIE tri-stimulus values, X, Y, Z, may be obtained by conventional processing of the functions (See, for example, the Vincent patent cited above and McLaughlin, U.S. Pat. No. 5,499,040, issued Mar. 12, 1996), thereby facilitating the use of the colorimeter for calibrating color monitors and color video and other displays.